Method for pattern reduction using a staircase spacer

ABSTRACT

Devices are made by self-aligned quad pitch patterning (SAQP), staircase patterning and double staircase patterning. Methods for making devices by self-aligned quad pitch patterning (SAQP) use a single spacer in the process. Methods for making devices by staircase patterning and double staircase patterning do not use a spacer. An intermediate process step called self-aligned double patterning (SADP) is used to double the pitch following the spacer deposition. A pattern is formed on a substrate, the pattern having ultra-fine resolutions by repeating the SADP step twice for pitch quadrupling and introducing a reversal layer to form a fine trench pattern and hole pattern. The pattern designs or pattern layouts have improved LER/LWR (line edge roughness and line width roughness respectively) for below 12 nm lines and trenches in order to create self-aligned cross pitch quad trenches.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Prov. Ser. No.63/029,072, entitled “Method For Pattern Reduction Using A StaircaseSpacer”, filed on May 22, 2020, and U.S. Prov. Ser. No. 63/028,619,“Method For Pattern Reduction Using Staircase Spacer” filed on May 22,2020. Each of the above applications is incorporated by referenceherein.

FIELD OF THE INVENTION

The present disclosure relates to microfabrication of integratedcircuits and semiconductor devices.

BACKGROUND

Semiconductor technologies are continually progressing to smallerfeature sizes of 14 nanometers and below. The continual reduction insizes of features, from which the foregoing elements are fabricated,places ever-greater demands on techniques used to form the features. Theconcept of “pitch” can be used to describe the sizing of these features.Pitch is the distance between the two identical points in two adjacentrepetitive features. Pitch reduction techniques, also termed “pitchmultiplication” as exemplified by “pitch doubling” and “pitchquadrupling,” can extend the capabilities of photolithography beyond thefeature size limitations. That is, conventional “multiplication” ofpitch by a certain factor actually involves reducing the pitch by thatfactor. Double patterning techniques (DPT) with 193 nm immersionlithography are considered to be promising techniques for the 22 nm nodeand beyond. Self-aligned spacer double patterning (SADP) has beenestablished as a routine pitch doubling process and has been adapted tohigh volume manufacturing of NAND flash memory devices.

Each of the aforementioned techniques suffers from one or more drawbackshindering their adoption. Accordingly, it is one object of the presentdisclosure to provide methods and systems for obtaining ultra-fineresolutions by repeating the SADP step twice for pitch quadrupling andintroducing a reversal layer to form a fine trench pattern and holepattern.

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

SUMMARY OF THE INVENTION

Aspects of the present disclosure methods and structures for obtainingultra-fine resolutions by repeating a pitch doubling step twice andintroducing a reversal layer to form a fine trench pattern and holepattern.

In a first embodiment, a method for patterning a substrate is describedcomprising depositing a stack of layers on the substrate, the stack oflayers comprising a first layer deposited on a second layer, the secondlayer deposited on at least one underlying layer; forming a first reliefpattern of lines from a first layer and a second layer, wherein therelief pattern of lines, defined by the first layer and the secondlayer, has a line-to-space ratio of 5:3 in that each line has an initialline width of five units while each space between lines has an initialspace width of three units, line edges of each line of the first layerbeing aligned with line edges of a corresponding line of the secondlayer; executing a first etch process, the first etch process being anisotropic etch that etches a material of the first layer without etchinga material of the second layer and without etching a material of the atleast one underlying layer, the first etch process being executed untilthe initial line width of each line from the first layer is reduced toone fifth of the initial line width, resulting in the lines of the firstlayer being centered on the lines of the second layer, the lines of thesecond layer maintaining a line width of five units; forming sidewallspacers on each line of the first layer and the second layer, thesidewall spacers being formed simultaneously on the first layer and thesecond layer; and transferring, by selective anisotropic etching, asecond relief pattern into at least one of the underlying layers, thesecond relief pattern defined by the sidewall spacers formed on thefirst layer and on the second layer, the second relief pattern formed inthe at least one underlying layer resulting in a line-to-space ratio of1:1, wherein each line and each space has a width of one unit.

In a second embodiment, a method for patterning a substrate isdescribed, the pattern having a line-to-space ratio of one-to-one,comprising forming a first stack of layers on the substrate, the firststack including a first layer deposited over the substrate, a secondlayer deposited over the first layer, a third layer deposited over thesecond layer and a fourth layer deposited over the third layer, each ofthe layers of the first stack having an initial width that is equal;forming a first relief pattern on the stack of layers, by executing afirst trimming etch process on the fourth layer, the first trimming etchprocess being an isotropic etch that etches material of the fourth layerwithout etching material of the second layer and without etchingmaterial of the third layer, the first trimming first etch process beingexecuted until the initial width of the fourth layer is reduced to afirst line of a first desired line width; executing a second trimmingetch process on the third layer, the second trimming etch process beingan isotropic etch that etches material of the third layer withoutetching material of the fourth layer and without etching material of thesecond layer, the second trimming etch process being executed until theinitial width of the third layer is reduced to a second line having aline width which is three times the first desired line width; executinga third trimming etch process on the second layer, the third trimmingetch process being an isotropic etch that etches material of the secondlayer without etching material of the first layer and the third layer,the third trimming etch process being executed until the initial widthof the second layer is reduced to a third line having a line width whichis five times the first desired line width; depositing a first fillmaterial on the fourth, third and second layers; etching a portion ofthe first fill material to expose a top of the first line; etching thefirst line through the fourth, third and second layers down to thesubstrate, thus forming a first central bore; removing, by etching, thethird layer and the fourth layer; depositing a second fill material inthe first central bore; removing a portion of the first fill material toexpose a part of the second layer; selectively etching through the partof the second layer not covered by the second fill material and throughportions of the first layer not covered by the first fill material;removing the first fill material and the second fill material; etchingremaining portions of the second layer, resulting in the first layerhaving a second relief pattern of four lines with line-to-space pitchratio of 1:1, wherein each line and each space has a width of one fifthof the first desired line width.

In a third embodiment, a method for patterning a substrate is described,the method comprising: forming a first stack of layers on a substrate,the first stack including a memorization layer deposited over thesubstrate, a first nitride layer deposited over the first memorizationlayer, a first amorphous carbon layer deposited over the first nitridelayer and a first oxide layer deposited over the first amorphous carbonlayer; forming a second stack of layers over the first stack of layers,the second stack including a second nitride layer deposited over thefirst oxide layer, a second amorphous carbon layer deposited on thesecond nitride layer, a second oxide layer deposited over the secondamorphous carbon layer, an organic planarization layer deposited overthe second oxide layer and a silicon anti-reflective coating depositedover the organic planarization layer, wherein each of the layers of thefirst stack and second stack having an initial width that is equal;depositing a photoresist relief pattern over the silicon anti-reflectivecoating; transferring, by selective anisotropic etching, the photoresistrelief pattern into the silicon anti-reflective coating, the organicplanarization layer, the second oxide layer, and the second amorphouscarbon layer, then removing the photoresist, the anti-reflective coatingand the organic planarization layer; executing a first trimming etchprocess on the second oxide layer, the first trimming etch process beingan isotropic etch that etches material of the second oxide layer withoutetching material of the second amorphous carbon layer and withoutetching material of the second nitride layer, the first trimming etchprocess being executed until the initial width of each line of thesecond oxide layer is reduced to one fifth of a line width of each lineof the photoresist relief pattern; executing a second trimming etchprocess on the second amorphous carbon layer, the second trimming etchprocess being an isotropic etch that etches material of the amorphouscarbon layer without etching material of the second oxide layer andwithout etching material of the second nitride layer, the secondtrimming etch process being executed until the initial width of eachline of the amorphous carbon layer is reduced to three fifths of theline width of each line of the photoresist relief pattern; depositing afirst fill material on the second oxide layer, the amorphous carbonlayer and the second nitride layer; etching a portion of the first fillmaterial to expose a top of the lines of the second oxide layer; etchingthe lines of the second oxide layer down through the second amorphouscarbon layer, then removing the first fill material, the lines of thesecond amorphous carbon layer forming a second relief pattern;transferring, by selective anisotropic etching, the second reliefpattern into the second nitride layer, the first oxide layer, and thefirst amorphous carbon layer, then removing the second amorphous carbonlayer and the second nitride layer; executing a fourth trimming etchprocess on the first oxide layer, the fourth trimming etch process beingan isotropic etch that etches material of the first oxide layer withoutetching material of the first amorphous carbon layer or material of thefirst nitride layer, the fourth trimming etch process being executeduntil a width of the lines of the first oxide is reduced to one third ofthe line width of the second relief pattern; depositing a second fillmaterial on the first oxide layer, the first amorphous carbon layer andthe first nitride layer; etching a portion of the second fill materialto expose a top of the lines of the first oxide layer; etching the linesof the first oxide layer down through the first amorphous carbon layer,then removing the second fill material, thus forming a third reliefpattern; transferring, by selective anisotropic etching, the thirdrelief pattern into the first nitride layer, then removing the firstamorphous carbon layer, thus forming a fourth relief pattern;transferring, by selective anisotropic etching, the fourth reliefpattern into the memorization layer, then removing the first nitridelayer, resulting in the memorization layer having a pattern of eightlines with line-to-space pitch ratio of 1:1, wherein each line and eachspace has a width of one eighth of the initial line width.

The order of discussion of the different steps as described herein hasbeen presented for the sake of clarity. In general, these steps can beperformed in any suitable order. Additionally, although each of thedifferent features, techniques, configurations, etc. herein may bediscussed in different places of this disclosure, it is intended thateach of the concepts can be executed independently of each other or incombination with each other. Accordingly, the present invention can beembodied and viewed in many different ways.

Note that this summary section does not specify every embodiment and/orincrementally novel aspect of the present disclosure or claimedinvention. Instead, this summary only provides a preliminary discussionof different embodiments and corresponding points of novelty overconventional techniques. For additional details and/or possibleperspectives of the invention and embodiments, the reader is directed tothe Detailed Description section and corresponding figures of thepresent disclosure as further discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A illustrates a stack of layers with a layer of photoresist ontop, according to certain embodiments.

FIG. 1B illustrates a relief pattern formed in the photoresist,according to certain embodiments.

FIG. 1C illustrates the transfer of the relief pattern into anunderlying layer, according to certain embodiments.

FIG. 1D illustrates the transfer of the relief pattern into a layerunderlying the layer of FIG. 1C., according to certain embodiments.

FIG. 1E illustrates the transfer of the relief pattern into an oxidelayer underlying the layer of FIG. 1D, according to certain embodiments.

FIG. 1F illustrates the transfer of the relief pattern into a nitridelayer underlying the layer of FIG. 1E, according to certain embodiments.

FIG. 1G illustrates trimming the oxide layer to one-fifth of its initialline width, according to certain embodiments.

FIG. 1H illustrates a spacer deposited over the substrate, according tocertain embodiments.

FIG. 1I illustrates the formation of sidewall spacers, according tocertain embodiments.

FIG. 1J illustrates removal of the oxide mandrel, according to certainembodiments.

FIG. 1K illustrates the nitride layer etched in the areas not protectedby spacers, according to certain embodiments.

FIG. 1L illustrates the substrate having the third relief patterntransferred into a memorization layer overlying the substrate, accordingto certain embodiments.

FIG. 1M illustrates an SEM photograph of the third relief pattern,according to certain embodiments.

FIG. 1N is a comparison of the relief pattern for positive (PTD) andnegative (NTD) processes, where (a) is accomplished by lithography, (b)is accomplished by supercritical CO₂ emulsion (SCE) and (c) by doublepatterning (DPT).

FIG. 2A illustrates a stack of layers on a substrate, with a photoresistlayer on top which has been patterned in a 5:3 pattern, having spaces of5 units to lines of 3 units, according to certain embodiments.

FIG. 2B illustrates a spacer formed on the substrate, according tocertain embodiments.

FIG. 2C, illustrates the substrate having portions of the spacer removedbetween the lines, leaving sidewall spacers on the lines and exposingthe tops of the lines, according to certain embodiments.

FIG. 2D illustrates the substrate with the photoresist removed, leavingthe sidewall spacers to form a second relief pattern, according tocertain embodiments.

FIG. 2E illustrates a fill material covering the substrate, according tocertain embodiments.

FIG. 2F illustrates removal of a portion of the fill material, leavingthe tops of the sidewall spacers exposed, according to certainembodiments.

FIG. 2G illustrates the substrate with the sidewall spacers removed,according to certain embodiments.

FIG. 2H illustrates the pattern of FIG. 2G transferred to an oxidelayer, according to certain embodiments.

FIG. 2I illustrates the substrate with the fill material removed,according to certain embodiments.

FIG. 2J illustrates the oxide layer trimmed to one-third its width,according to certain embodiments.

FIG. 2K illustrates a fill material covering the substrate, according tocertain embodiments.

FIG. 2L illustrates the exposure of the tops of the oxide lines,according to certain embodiments.

FIG. 2M illustrates the substrate with the oxide lines and portions ofthe nitride layer below the oxide lines removed, according to certainembodiments.

FIG. 2N illustrates the one-to-one pattern of lines and spaces with thefill material removed, according to certain embodiments.

FIG. 2O illustrates is a comparison of the relief pattern for positive(PTD) and negative (NTD) processes, where (a) is accomplished bylithography, (b) is accomplished by supercritical CO₂ emulsion (SCE) and(c) by double patterning (DPT).

FIG. 3A illustrates an initial stack of layers for a method whichquadruples a single line, according to certain embodiments.

FIG. 3B illustrates a trimmed stack having a first line of one unit, asecond line of three units, a third line of five units on top of amemorization layer, which is on top of a substrate, according to certainembodiments.

FIG. 3C illustrates a first fill material covering the substrate withthe top of first line exposed, according to certain embodiments.

FIG. 3D illustrates the substrate with the first line etched down to thesubstrate, according to certain embodiments.

FIG. 3E illustrates the substrate with the second line removed,according to certain embodiments.

FIG. 3F illustrates a second fill material deposited in the cavityformed by etching the first and second lines from the substrate,according to certain embodiments.

FIG. 3G illustrates a removal of a portion of the first fill material toexpose a portion of the third line, according to certain embodiments.

FIG. 3H illustrates removal of the third line and the portion of thememorization layer below the third line, according to certainembodiments.

FIG. 3I illustrates the substrate with the second fill material removed,according to certain embodiments.

FIG. 3J illustrates the quadrupled first line pattern having a 1:1 ratioof lines and spaces, according to certain embodiments.

FIG. 4A illustrates a double stack of layers formed on a substrate,according to certain embodiments.

FIG. 4B illustrates a 1:1 pattern formed in a photoresist layer,according to certain embodiments.

FIG. 4C illustrates the etch transfer of the 1:1 pattern into the nextfour underlying layers, according to certain embodiments.

FIG. 4D illustrates the removal of two of the overburden layers,according to certain embodiments.

FIG. 4E a first staircase with top lines trimmed to one fifth of theiroriginal width, according to certain embodiments.

FIG. 4F illustrates reverse image organic planarization covering the twotop lines, according to certain embodiments.

FIG. 4G illustrates the substrate etched through the top lines,according to certain embodiments.

FIG. 4H illustrates removal of the organic planarization material,according to certain embodiments.

FIG. 4I illustrates transfer into underlying layers, according tocertain embodiments.

FIG. 4J illustrates removal of the top two layers, according to certainembodiments.

FIG. 4K illustrates a second staircase step with top lines trimmed toone third of their original width, according to certain embodiments.

FIG. 4L illustrates reverse image organic planarization covering the twotop lines of FIG. 4K, according to certain embodiments.

FIG. 4M illustrates the substrate top two lines etched in regions notcovered by the reverse image organic planarization, according to certainembodiments.

FIG. 4N illustrates removal of the overburden layer, according tocertain embodiments.

FIG. 4O illustrates transfer of the pattern of FIG. 4N into a hardmasklayer, according to certain embodiments.

FIG. 4P illustrates removal of the overburden layer of FIG. 4O,according to certain embodiments.

FIG. 4Q illustrates transfer of the pattern into a memorization layer,according to certain embodiments.

FIG. 4R illustrates the substrate with all layers above the memorizationlayer removed, according to certain embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

Aspects of the present disclosure describe process flows with a patterndesigns or pattern layouts having improved LER/LWR (line edge roughnessand line width roughness respectively) for below 12 nm lines andtrenches in order to create self-aligned cross pitch quad trenches. Theinitial pattern is obtained by the X-Y double line exposures. Reversematerial is applied on the initial pattern and subsequent etchingprocess converts each initial trench pattern to a line.

Techniques herein provide a patterning flow that provides improved LERand LWR at least for lines and trenches of 12 nm and below. For ease indescribing embodiments, reference will be made to specific materials forparticular layers, but it should be understand that many alternatematerials and combinations can be selected instead. Etch properties ofvarious materials are conventionally understood and particular materialscan be selected to provide etch selectivity (etching one materialwithout substantially etching another material.

Aspects of the present disclosure describe devices made by self-alignedquad pitch patterning (SAQP) and methods for making devices byself-aligned quad pitch patterning (SAQP) using a single spacer in theprocess. An intermediate process step called self-aligned doublepatterning (SADP) is used to double the pitch following the spacerdeposition.

In a first process flow, shown in FIG. 1A-FIG. 1L, layers are stackedwith resist on top. A lithographic exposure is executed with aline-to-space pitch ratio of 5:3. The pattern is transferred to multipleunderlying layers. An isotropic oxide etch is executed selective to anunderlying layer to reduce the initial pattern width to ⅕ its initialline thickness. Spacers are formed on the reduced-thickness line as wellas on the thicker underlying layer. This provides spacers on differentplanes to be transferred to an underlying layer.

FIG. 1A illustrates a stack of layers with a layer of photoresist on topformed on a substrate 102. A memorization layer 104 can be a hardmask ormetal hard mask and is formed over the substrate 102. The memorizationlayer 104 may include any one of TEOS, low temperature oxide, deepultraviolet light absorbing oxide, a low-temperature amorphous siliconor poly silicon, boron, germanium, copper, an inorganic metal or thelike. An etch stop layer 106 can also act as a memorization layer, andis formed over the memorization layer 104. The etch stop layer 106 canbe formed of silicon nitride, silicon carbide, silicon carbonitride, andthe like. A silicon nitride layer (SiN) 108 (layer 108 may alternativelybe a titanium nitride layer (TiN)) is formed on the etch stop layer 106,an oxide layer 110 (silicon dioxide or titanium dioxide) is formed onthe SiN layer, an amorphous carbon layer 112 is formed on the oxidelayer, a silicon-containing anti-reflective coating 114 (Si-ARC or BARC)is formed on the amorphous carbon layer 112, and the layer ofphotoresist 116 is deposited on top. Note that additional interfaciallayers and intermediate layers can be included. Each upper layer isselective to the underlying layer for etching.

As shown in FIG. 1B, the substrate is exposed to a pattern of actinicradiation that defines a line-to-space pitch ratio of 5:3. That is,lines are five units wide and spaces between lines are three units wide.The latent pattern is developed using a solvent to etch a relief patternwith this 5:3 ratio in photoresist 116. With the 5:3 pitch patternformed, this pattern can be transferred into one or more underlyingtarget layers, such as by anisotropic (directional) plasma-basedreactive etching.

In FIG. 1C, the 5:3 pattern is transferred into the Si-ARC layer 114.

In FIG. 1D, the 5:3 pattern is transferred into the amorphous carbonlayer 112 and the Si-ARC layer 114 and photoresist 116 are removed.

In FIG. 1E, the 5:3 pattern is transferred into the oxide layer 110 andthe amorphous carbon layer 112 is removed.

In FIG. 1F, the 5:3 pattern is transferred into the SiN layer 108,retaining the oxide layer 110 on the top of the SiN layer.

Any remaining layers above the oxide layer are removed. As shown in FIG.1G, a first isotropic (non-directional) etch is executed that reducesthe line widths of the oxide lines to one fifth of the initial linewidth. Thus, ⅖ of the initial line width can be etched away from the topand each side of a given line of the oxide 110. This oxide etch isselective to the SiN layer 108 and the etch stop layer 106.

In FIG. 1H, a spacer deposition is then executed on the substrate. Thespacer deposition conformally deposits a film for defining spacers 118on the substrate. Thus this spacer deposition follows the 5:3 patternratio of the SiN layer 108, as well as the ⅕ line size/mandrel size ofthe oxide layer 110 still remaining on the SiN layer 108. The spacer maybe formed from silicon, silicon dioxide, silicon oxycarbide (SiOC),silicon nitride (SiN), or the like.

In FIG. 1I, a spacer etch back process is executed that directionallyetches the spacer material down to the top of oxide layer 110 and cutsbetween SiN layer 108 lines, thus clearing spacer material fromhorizontal surfaces and leaving sidewall spacers on sidewalls of oxide110 and SiN layer 108 mandrels on the substrate.

The oxide mandrels can then be removed from between the spacer sidewallsas shown in FIG. 1J, leaving the spacer material above the SiN layer 108and spacer sidewalls on either side of the SiN layer 108.

An anisotropic etch can be executed that etches portions of the SiNlayer not covered by spacers as shown in FIG. 1K. The pattern defined byspacers 118 on two or more planes can be transferred into one or moreunderlying layers such as the etch stop layer 106 and/or memorizationlayer 104.

FIG. 1L shows that the three original lines etched in photoresist 116shown in FIG. 1B have quadrupled to twelve evenly spaced lines.Additional patterning can then be continued from this point to furtherreduce the line widths if desired.

FIG. 1M is a representation of an SEM photograph of the pattern showingthe line and space widths of an intermediate step of the isotropic etch.The line widths taper, but widths of each line are each approximately 12nm.

FIG. 1N shows a top down view comparing the lines formed by positivephotoresist (PTD) and negative photoresist (NTD) development. Resultsare compared for the (a) the lithographic process of the presentdisclosure to previous methods where the photoresist was removed by (b)supercritical CO₂ emulsion (SCE) and (c) by double patterning DPT. Thelithographic process of the present disclosure clearly shows smallerline widths and more even spacing than the SCE and DPT methods.Additionally, the lithographic method for the negative photoresist rowappears to show more even line widths than the lithographic methodpositive photoresist line widths.

In a second process flow, layers are stacked on a substrate with resiston top. A lithographic exposure and development process is used to forma relief pattern of lines. This can include lines formed on a firstlayer, the first layer on a second layer, and the second layer on anunderlying layer or substrate. By way of a non-limiting example, thelines can be formed of photoresist 216, with the photoresist formed on(or over any interfacial or intermediate layers), then over an oxidelayer 210, which in turn is formed on a layer of nitride 208, such assilicon nitride, SiN, which is over a substrate 202 as shown in FIG. 2A.The relief pattern is of lines having a line-to-space ratio of 3:5 inthat lines have a width of three units relative to spaces having a widthof five units. FIG. 2A shows a cross sectional substrate segment with3:5 pitch ratio lines on a substrate stack of substrate layer 202,nitride layer 208 and oxide layer 210.

In FIG. 2B, spacer deposition is executed with spacers 222 having athickness equal to one third of the line thickness. This is a conformaldeposition in that a thickness on all surfaces (horizontal and vertical)is generally uniform.

In FIG. 2C, a “spacer open” etch is then executed. This is ananisotropic/directional etch that etches a thickness of the spacer toremove spacer material from horizontal surfaces, leaving sidewallspacers on sidewalls of the photoresist lines. The spacer 222 is etchedbetween the photoresist lines, down to the oxide layer 210, leavingspacers on either side of the photoresist. The spacer 222 is alsoremoved from the tops of the photoresist lines to expose the photoresist216.

In FIG. 2D, the photoresist mandrel is removed from between the spacer222 sidewalls. This leaves the sidewall spacers on the substrate as anew relief pattern.

In FIG. 2E, a fill material 224 is deposited on the substrate so that itfills the spaces between lines of the spacer 222. The fill material 224may comprise at least one of amorphous carbon, silicon oxycarbide(SiOC), silicon nitride (SiN), an organic planarization layer (OPL),titanium nitride (TiN), and high-density plasma (HDP) nitride. The fillmaterial 224 is preferably self-planarizing, and capable of being etchedback.

In FIG. 2F, a directional etch is applied which uncovers the tops of thesidewall spacers. Initially, the fill can result in an overcoat. Thefill material 224 can be an organic reversal planarizing material.

In FIG. 2G, the overburden portion of the spacer 222 is then removed bya planarization process, such as a precision etch back. The sidewallspacers are then removed from the substrate. This results in the fillmaterial 224 defining a second relief pattern, which is the reverse ofthe sidewall spacer pattern.

In FIG. 2H, the second relief pattern is transferred into the oxidelayer 210, by etching through the first layer (oxide layer 210) down tothe second layer (nitride layer 208). Stacks are formed by the oxide 210covered by fill material 224 with open spaces between the stacks wherethe spacer was removed.

In FIG. 2I, the fill material 224 and the nitride 208 are removed by anetching processes, leaving the oxide layer 210 as the relief pattern.

In FIG. 2J, the nitride layer 208 is etched down to the top of thesubstrate layer 202 in the regions not protected by the oxide layer 210.Then the oxide upper lines are trimmed by an isotropic trimming etch.The etch is continued until the width of each of the lines of the firstlayer is one third its initial width. Thus, an initial line of threeunits is reduced to one unit in width, centered on the second layerlines, which still have a width of three units.

In FIG. 2K, a second fill material is then deposited over the reliefpattern, which can be the same planarizing fill material as the firstfill material 224, and is also labelled 224 in FIG. 2K to FIG. 2M.

In FIG. 2L, the overburden of fill material is then removed to uncovertop surfaces of the trimmed lines of oxide 210 of the first layer. Thefill material 224 still covers top surfaces of the second layer (nitride208) lines.

In FIG. 2M, the trimmed (oxide layer 210) lines are etched out, leavingthe fill material 224 to function as a relief pattern and an etch maskto protect all but the center single width of the nitride layer 208.Removing the first layer uncovers a center portion of the lines of thesecond layer. This center portion opening between the lines is a unit inwidth.

In FIG. 2N, the nitride layer 208 is then etched by directional etchingdown to the substrate 202 layer and all remaining fill material 224 isremoved, leaving a pattern of nitride lines on the substrate.Effectively, the trimmed lines are reversed and transferred intounderlying lines to result in a line-to-space ratio of 1:1.

FIG. 2O, shows a top down view comparing the lines formed by positivephotoresist (PTD) and negative photoresist (NTD) development. Resultsare compared for the (a) the lithographic process of the presentdisclosure to previous methods where the photoresist was removed by (b)supercritical CO2 emulsion (SCE) and (c) by double patterning (DPT). Thelithographic process of the present disclosure clearly shows smallerline width and more even spacing than the SCE and DPT methods.Additionally, the lithographic method on the negative photoresist rowappears to show more even line widths than the lithographic methodpositive photoresist line widths.

In a third process flow, a double stack staircase process is describedwhich quadruples a single line stack. Layers are stacked on a substratewith resist on top. A lithographic exposure and development process isused to form a relief pattern of lines.

The double stack staircase may start at the step previously shown asFIG. 1G. FIG. 3A shows a single line section of the three lines shown inFIG. 1G. At this point, an oxide layer 310, which may be SiO₂, has beenetched to a line of one unit in width, and the underlying nitride layer308, which may be SiN or TiN, has been etched to a width of 3 units. Theremaining stack is an etch stop layer, 306, a memorization layer 304 anda substrate 302, which is a wafer. The memorization layer 304 can be ahardmask or metal hard mask and is formed over the substrate 302. Theetch stop layer 306 can also act as a memorization layer, and is formedover the memorization layer 304. The etching may be performed byanisotropic (directional) plasma-based reactive etching.

In FIG. 3B, a selective etch is executed which directionally etches etchstop layer 306 to a width of five units. A “staircase” structure withsteps of one unit in width is now centered about the line formed inoxide layer 310.

In FIG. 3C, the structure of FIG. 3B is covered with a fill layer 324,leaving only the tops of oxide layer 310 exposed. The fill layer 324 canbe an organic reversal planarizing material.

In FIG. 3D, the oxide layer 310, the nitride layer 308, the etch stoplayer 306 and the memorization layer 304 are etched down to thesubstrate layer, splitting the structure into two parts. The fill layer324 is etched down below the top of the nitride layer, leaving the topsof the nitride layer halves exposed.

In FIG. 3E, the remaining nitride layer 308 portions have been removedby selective etching.

In FIG. 3F, the central cavity formed by etching the oxide layer andunderlying layers plus the nitride layer is filled with photoresist 316to just below the top of fill layer 324.

In FIG. 3G, etch stop layer 306 and fill layer 324 are selectivelyetched to open etch stop layer 306.

In FIG. 3H, the open portion of etch stop layer and the portion of thememorization layer 304 are etched down to the substrate layer 302. Theremaining portion of etch stop layer 306 has been protected by thephotoresist layer 318 from the etch process and the remaining portion ofmemorization layer 304 has been protected by fill layer 324 from theetch process. Thus, the stack formed by memorization layer 304 coveredby the fill material 324 defines a line.

In FIG. 3I, the photoresist mandrel is removed from the space betweenthe center lines, leaving four lines, where the outer two are coveredwith fill material 324 and the inner two are covered by etch stop layer306.

In FIG. 3J, the fill material 324 and etch stop layer 306 are removedfrom the lines, leaving the final structure of four evenly spaced lineswith a line-to-space ratio of 1:1. Thus, the single line of FIG. 3A hasbeen quadrupled to four evenly spaced lines using two fill processes andno spacers.

The double stack staircase process can be repeated by forming a secondunderlying stack of layers between the first stack of layers and thesubstrate, transferring the structure of four evenly spaced lines with aline-to-space ratio of 1:1 into an underlying layer and repeating thedouble stack staircase process. This embodiment will form eight linesfrom an initial single line of the first relief pattern.

A fourth process which achieves finer line widths is described in FIG.4A-FIG. 4R. The processes described above can be repeated in a stackhaving two sets of layers comprising the nitride layer, the amorphouscarbon layer and the oxide layer. An organic planarization layer coversthe two sets of layers and an Si-ARC layer covers the organicplanarization layer. The fourth process flow describes a line structurewhich starts with the stack of repeating layers. For the purpose ofdescribing the fourth process, the 5:3 pattern of the first process isused as a first set of layers. The fourth stack may have a substratelayer 402, a memorization layer 404, a first nitride layer 408-1, afirst amorphous carbon layer 412-1, a first oxide layer 410-1, a secondnitride layer 408-2, a second amorphous carbon layer 410-2, a secondoxide layer 410-2, an organic planarization layer 424, an Si-ARC layer414-2 and a top layer of photoresist 416. The materials of the layersare substantially the same as the materials described above for FIG.1A-FIG. 1L.

As shown in FIG. 4B, the photoresist layer is exposed to a pattern ofactinic radiation that defines a line-to-space pitch ratio of 7:1. Thatis, for each unit width, lines are ⅞^(th) of a unit wide and spacesbetween lines are ⅛^(th) of a unit wide. The latent pattern is developedusing a solvent to etch a relief pattern with this 7:1 ratio inphotoresist layer 416. With the 7:1 pitch pattern formed, this patterncan be transferred into one or more underlying target layers, such as byanisotropic (directional) plasma-based reactive etching.

As shown in FIG. 4C, the openings in the photoresist pattern areanisotropically etched through the Si-ARC layer 414, the organicplanarization layer 424, the second oxide layer 410-2 and the secondamorphous carbon layer 412-2.

In FIG. 4D, Si-ARC layer 414 and the organic planarization layer 424 areremoved by an etching process, leaving the second oxide layer 410-2 andthe second amorphous carbon layer 412-2 as the relief pattern forprocessing the underlying first set of layers.

In FIG. 4E, each line of second oxide layer 410-2 is trimmed to oneseventh its width by an isotropic (non-directional) etch. Thus, 3/7 ofthe initial line width can be etched away each side of a given line ofthe oxide layer 410-2. Each line of the oxide layer 410-2 now has awidth of ⅛ of the initial pitch. This etch is selective to the oxidelayer 410-1 and does not etch the second amorphous carbon layer 412-2 orthe underlying second nitride layer 408-2.

In FIG. 4F, a fill material is deposited on the substrate, leaving thetops of the lines formed by the second oxide layer 410-2. The fillmaterial may be an organic reverse image planarization material.

In FIG. 4G, the pattern is etched through the second oxide layer 410-2lines down to the second nitride layer 412-2.

In FIG. 4H, the fill material is removed, leaving a four line pattern inthe second amorphous carbon layer 412-2.

In FIG. 4I, the second amorphous carbon layer 412-2 acts as an etch stoplayer to protect underlying layers during an isotropic etch throughsecond nitride layer 408-2, first oxide layer 410-1 and first amorphouscarbon layer 412-1.

In FIG. 4J, the second amorphous carbon layer 412-2 and second nitridelayer 408-2 are removed.

In FIG. 4K, the substrate is exposed to a pattern of actinic radiationthat defines a line-to-space pitch ratio of 1:3. That is, lines are oneunit wide and spaces between lines are three units wide. The latentpattern is developed using a solvent to etch a relief pattern with this1:3 ratio in the first oxide layer 410-1. With the 1:3 pitch patternformed, this pattern can be transferred into one or more underlyingtarget layers, such as by anisotropic (directional) plasma-basedreactive etching.

In FIG. 4L, a fill material 424, which may be an organic planarizationmaterial, is formed over the pattern of FIG. 4K, leaving the tops of thefirst oxide layer 410-1 exposed.

In FIG. 4M, an anisotropic etch is executed that etches through thefirst oxide layer 410-1 and into portions of first amorphous carbonlayer 412-1 not covered by fill material 424.

In FIG. 4N, the remaining fill material 424 is removed, leaving thelines formed by first amorphous carbon layer 412-1.

In FIG. 4O, the pattern is transferred into the first nitride layer408-1.

In FIG. 4P, the first amorphous carbon layer 412-1 is removed.

In FIG. 4Q, the pattern of FIG. 4P is transferred into the memorizationlayer 404.

In FIG. 4R, the remaining portions of layer first nitride layer 408-1are removed by etching or planarizing, leaving a 1:1 line/space patternof four lines resulting from each original one line of FIG. 4B. Theinitial center line shown in FIG. 4B has undergone two staircaseprocesses leaving four lines with a 1:1 space to line ratio.Accordingly, techniques herein can provide pitch reduction (staircasepatterning) without using spacers. This can improve LER/LWR, eliminateoverlay errors from stitching layers, as well as provide efficiencies inmanufacturing.

In the preceding description, specific details have been set forth, suchas a particular geometry of a processing system and descriptions ofvarious components and processes used therein. It should be understood,however, that techniques herein may be practiced in other embodimentsthat depart from these specific details, and that such details are forpurposes of explanation and not limitation. Embodiments disclosed hereinhave been described with reference to the accompanying drawings.Similarly, for purposes of explanation, specific numbers, materials, andconfigurations have been set forth in order to provide a thoroughunderstanding. Nevertheless, embodiments may be practiced without suchspecific details. Components having substantially the same functionalconstructions are denoted by like reference characters, and thus anyredundant descriptions may be omitted.

Various techniques have been described as multiple discrete operationsto assist in understanding the various embodiments. The order ofdescription should not be construed as to imply that these operationsare necessarily order dependent. Indeed, these operations need not beperformed in the order of presentation. Operations described may beperformed in a different order than the described embodiment. Variousadditional operations may be performed and/or described operations maybe omitted in additional embodiments.

“Substrate” or “target substrate” as used herein generically refers toan object being processed in accordance with the invention. Thesubstrate may include any material portion or structure of a device,particularly a semiconductor or other electronics device, and may, forexample, be a base substrate structure, such as a semiconductor wafer,or a layer on or overlying a base substrate structure such as a thinfilm. Thus, substrate is not limited to any particular base structure,underlying layer or overlying layer, patterned or un-patterned, butrather, is contemplated to include any such layer or base structure, andany combination of layers and/or base structures. The description mayreference particular types of substrates, but this is for illustrativepurposes only.

Those skilled in the art will also understand that there can be manyvariations made to the operations of the techniques explained abovewhile still achieving the same objectives of the invention. Suchvariations are intended to be covered by the scope of this disclosure.As such, the foregoing descriptions of embodiments of the invention arenot intended to be limiting. Rather, any limitations to embodiments ofthe invention are presented in the following claims.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A method of patterning a substrate, the method comprising: providinga substrate; depositing a stack of layers on the substrate, the stack oflayers comprising a first layer deposited on a second layer, the secondlayer deposited on at least one of a first set of underlying layers;forming a first relief pattern of lines over the first layer and thesecond layer, the first layer formed on the second layer, the secondlayer formed on the at least one underlying layer, the first reliefpattern of lines having a line-to-space ratio of 3:5 in that lines havean initial line width of three units relative to spaces having aninitial space width of five units; forming sidewall spacers on sidewallsof the first relief pattern of lines, the sidewall spacers having athickness equal to one third the initial line width, thereby having arelative thickness of one unit; removing, by selective anisotropicetching, a material forming the first relief pattern of lines from thesubstrate and depositing a first fill material between the sidewallspacers; removing the sidewall spacers from the substrate resulting inthe first fill material defining a second relief pattern, the secondrelief pattern having a line-to-space pitch ratio of 3:1 in that lineshave a width of three units relative to spaces having a width of oneunit; transferring, by selective anisotropic etching, the second reliefpattern into the first layer and into the second layer; removing, byplanarization, the first fill material from the substrate; executing afirst trimming etch process, the first trimming etch process being anisotropic etch that etches material of the first layer without etchingmaterial of the second layer and without etching material of anunderlying layer, the first trimming etch process being executed untilan initial line width of lines from the first layer is reduced to onethird of the initial line width, resulting in lines of the first layerbeing centered on lines of the second layer, the lines of the secondlayer maintaining the initial width of three units; depositing a secondfill material between lines of the first layer and the second layer suchthat top surfaces of lines of the second layer are covered while topsurfaces of lines of the first layer are uncovered; removing a materialof the first layer from the substrate; forming a third relief pattern byremoving, by selective anisotropic etching, a first portion of amaterial of the second layer which is not covered by the second fillmaterial, transferring, by selective anisotropic etching, the thirdrelief pattern into lines of the second layer, resulting in the secondlayer having a line-to-space pitch ratio of 1:1, wherein each line andeach space has a width of one unit.
 2. The method of claim 1, whereinthe first fill material and the second fill material are organicreversal self-planarizing materials.
 3. The method of claim 1, furthercomprising: performing the planarization by a precision etch backprocess.
 4. The method of claim 1, further comprising: forming the firstrelief pattern by: depositing a photoresist over the first layer; andexposing the photoresist to a pattern of actinic radiation that definesthe line-to-space pitch ratio of 3:5.
 5. The method of claim 4, whereinthe photoresist is one of a positive photoresist and a negativephotoresist.
 6. The method of claim 1, further comprising: forming thefirst layer from one of silicon dioxide or titanium dioxide; and formingthe second layer from one of silicon nitride or titanium nitride.
 7. Themethod of claim 1, wherein each line and each space of the second reliefpattern has a width in a range of 10 nm to 21 nm.
 8. The method of claim1, further comprising: forming the first set of underlying layers bydepositing a first underlying layer on the substrate; depositing asecond underlying layer on the first underlying layer; depositing athird underlying layer on the second underlying layer; and depositing afourth underlying layer on the third underlying layer.
 9. The method ofclaim 8, further comprising: transferring, by selective anisotropicetching, the third relief pattern into the fourth underlying layer, thethird underlying layer and the second underlying layer; removing, byplanarization, the second layer; executing a second trimming etchprocess, the second trimming etch process being an isotropic etch thatetches material of the fourth underlying layer without etching materialof the third underlying layer and without etching material of the secondunderlying layer, the first trimming etch process being executed until aline width of lines from the fourth underlying layer is reduced to onefifth of an initial line width of one unit, resulting in lines of thefourth underlying layer being centered on lines of the third underlyinglayer, the lines of the third underlying layer and the second underlyinglayer maintaining the initial line width of one unit; and executing athird trimming etch process on the third underlying layer, the thirdtrimming etch process being an isotropic etch that etches material ofthe third underlying layer without etching material of the fourthunderlying layer and without etching material of the second underlyinglayer, the second trimming etch process being executed until the linewidth of the third underlying layer is reduced to three fifths of theinitial width of one unit, resulting in lines of the third underlyinglayer being centered on lines of the second underlying layer, the linesof the second underlying layer maintaining the initial line width of oneunit.
 10. The method of claim 9, further comprising: depositing a thirdfill material on lines of the fourth underlying layer, lines of thethird underlying layer, lines of the second underlying layer and onlines of the first underlying layer; etching the third fill material toexpose a top of the lines of the fourth underlying layer; etching thelines of the fourth underlying layer through the fourth underlyinglayer, the third underlying layer, the second underlying layer and thefirst underlying layer down to a top of the substrate, forming a centralbore; removing a portion of the third fill material from substrate toexpose a top of the lines of the third underlying layer; removing, byselective anisotropic etching, the lines of third underlying layer,without etching the third fill material; depositing a fourth fillmaterial in the central bore and over exposed portions of the secondunderlying layer; removing the third fill material to expose portions ofthe lines of the second underlying layer not covered by the fourth fillmaterial; selectively etching through the exposed portions of the linesof the second underlying layer not covered by the second fill materialdown through the first underlying layer to the top of the substrate;removing the fourth fill material and the third fill material; etchingremaining portions of the second layer, resulting in each line of thefirst underlying layer having a line-to-space pitch ratio of 1:1,wherein each line and each space of the first underlying layer has awidth of one fifth of one unit.
 11. The method of claim 10, wherein eachline and each space of the first underlying layer has a width in a rangeof 2 to 5 nm.
 12. The method of claim 1, further comprising: forming thefirst set of underlying layers by depositing a first memorization layeron the substrate; depositing a first etch stop layer on the firstmemorization layer; depositing a first nitride layer on the first etchstop layer; depositing a first oxide layer on the first nitride layer;and depositing a first amorphous carbon layer on the first oxide layer.13. The method of claim 12, further comprising: transferring, byselective anisotropic etching, the second relief pattern into the firstamorphous carbon layer; removing, by planarization, the first layer andthe second layer; transferring, by selective anisotropic etching, thesecond relief pattern into the first oxide layer; removing, byplanarization, the first amorphous carbon layer; transferring, byselective anisotropic etching, the second relief pattern into the firstnitride layer; removing, by planarization, the first oxide layer;transferring, by selective anisotropic etching, the second reliefpattern into the first etch stop layer; removing, by planarization, thefirst nitride layer; transferring, by selective anisotropic etching, thesecond relief pattern into the first memorization layer; and removing,by planarization, the first etch stop layer, resulting in the firstmemorization layer having the line-to-space pitch ratio of 1:1, whereineach line and each space has a width of one unit.
 14. The method ofclaim 13, further comprising: forming a second set of underlying layersbetween the substrate and the first memorization layer by: depositing asecond memorization layer over the substrate; depositing a second etchstop layer over the second memorization layer; depositing a secondnitride layer over the second etch stop layer; depositing a second oxidelayer over the second nitride layer; and depositing a second amorphouscarbon layer over the second oxide layer.
 15. The method of claim 14,transferring, by selective anisotropic etching between the lines of thefirst memorization layer, the line-to-space pitch ratio of 1:1 into thesecond amorphous carbon layer; removing, by planarization, the firstmemorization layer; transferring, by selective anisotropic etchingbetween the lines of the second amorphous carbon layer, theline-to-space pitch ratio of 1:1 into the second oxide layer; executinga second etch process, the second etch process being an isotropic etchthat etches the second amorphous carbon layer without etching the secondoxide layer and without etching the second nitride layer, the secondetch process being executed until a width of each line from the secondamorphous carbon layer is reduced to one fifth of one unit, resulting inthe lines of the second amorphous carbon layer being centered on thelines of the second oxide layer, the lines of the second oxide layermaintaining a line width of one unit; depositing a second spacer overthe lines of the second amorphous carbon layer, the lines of the secondoxide layer and the second nitride layer; forming second sidewallspacers by etching the second spacer to open portions between the linesof the second amorphous carbon layer and the lines of the second oxidelayer; removing, by selective anisotropic etching, the second amorphouscarbon layer between the second sidewall spacers without etching thesidewall spacers; forming a third relief pattern by removing, byselective anisotropic etching, a first portion of the second oxide layerbetween the second sidewall spacers without removing a second portion ofthe second oxide layer beneath the second sidewall spacers of the secondamorphous carbon layer; transferring, by selective anisotropic etching,the third relief pattern into the second nitride layer and the secondetch stop layer; removing, by planarization, the second spacers, thesecond portion of the second oxide layer and the second nitride layer;and transferring, by selective anisotropic etching, the third reliefpattern into the second memorization layer, the third relief patternresulting in a line-to-space pitch ratio of 1:1, wherein each line andeach space has a width of one fifth of one unit.
 16. The method of claim15, wherein the third relief has a line width in a range of 2 to 5 nm.17. A method of patterning a substrate, the method comprising: forming afirst stack of layers on the substrate, the first stack including afirst layer deposited over the substrate, a second layer deposited overthe first layer, a third layer deposited over the second layer and afourth layer deposited over the third layer, each of the layers of thefirst stack having an initial width that is equal; forming a firstrelief pattern on the stack of layers, by: executing a first trimmingetch process on the fourth layer, the first trimming etch process beingan isotropic etch that etches material of the fourth layer withoutetching material of the second layer and without etching material of thethird layer, the first trimming first etch process being executed untilthe initial width of the fourth layer is reduced to a first line of afirst desired line width; executing a second trimming etch process onthe third layer, the second trimming etch process being an isotropicetch that etches material of the third layer without etching material ofthe fourth layer and without etching material of the second layer, thesecond trimming etch process being executed until the initial width ofthe fourth layer is reduced to a second line having a line width whichis three times the first desired line width; executing a third trimmingetch process on the second layer, the third trimming etch process beingan isotropic etch that etches material of the second layer withoutetching material of the first layer and the third layer, the thirdtrimming etch process being executed until the initial width of thesecond layer is reduced to a third line having a line width which isfive times the first desired line width; depositing a first fillmaterial on the fourth, third and second layers; etching a portion ofthe first fill material to expose a top of the first line; etching thefirst line through the fourth, third and second layers down to thesubstrate, thus forming a first central bore; removing, by etching, thethird layer and the fourth layer; depositing a second fill material inthe first central bore; removing a portion of the first fill material toexpose a part of the second layer; selectively etching through the partof the second layer not covered by the second fill material and throughportions of the first layer not covered by the first fill material;removing the first fill material and the second fill material; andremoving, by etching, the second layer, resulting in the first layerhaving a second relief pattern of four lines with line-to-space pitchratio of 1:1, wherein each line and each space has a width of one fifthof the first desired line width.
 18. The method of claim 17, whereineach line and each space of the second relief pattern has a width in arange of 10 nm to 21 nm.
 19. A method of patterning a substrate, themethod comprising: forming a first stack of layers on a substrate, thefirst stack including a memorization layer deposited over the substrate,a first nitride layer deposited over the memorization layer, a firstamorphous carbon layer deposited over the first nitride layer and afirst oxide layer deposited over the first amorphous carbon layer;forming a second stack of layers over the first stack of layers, thesecond stack including a second nitride layer deposited over the firstoxide layer, a second amorphous carbon layer deposited on the secondnitride layer, a second oxide layer deposited over the second amorphouscarbon layer, an organic planarization layer deposited over the secondoxide layer and a silicon anti-reflective coating deposited over theorganic planarization layer, wherein each of the layers of the firststack and second stack have equal initial width; depositing aphotoresist relief pattern of lines over the silicon anti-reflectivecoating; transferring, by selective anisotropic etching, the photoresistrelief pattern of lines into the silicon anti-reflective coating, theorganic planarization layer, the second oxide layer, and the secondamorphous carbon layer, then removing the photoresist, theanti-reflective coating and the organic planarization layer; executing afirst trimming etch process on the second oxide layer, the firsttrimming etch process being an isotropic etch that etches material ofthe second oxide layer without etching material of the second amorphouscarbon layer and without etching material of the second nitride layer,the first trimming etch process being executed until the initial widthof each line of the second oxide layer is reduced to one seventh of aline width of each line of the photoresist relief pattern; executing asecond trimming etch process on the second amorphous carbon layer, thesecond trimming etch process being an isotropic etch that etchesmaterial of the amorphous carbon layer without etching material of thesecond oxide layer and without etching material of the second nitridelayer, the second trimming etch process being executed until the initialwidth of each line of the amorphous carbon layer is reduced to threeeighths of the line width of each line the photoresist relief pattern;depositing a first fill material on the second oxide layer, theamorphous carbon layer and the second nitride layer; etching a portionof the first fill material to expose a top of the lines of the secondoxide layer; etching the lines of the second oxide layer down throughthe second amorphous carbon layer, then removing the first fillmaterial, the lines of the second amorphous carbon layer forming asecond relief pattern; transferring, by selective anisotropic etching,the second relief pattern into the second nitride layer, the first oxidelayer, and the first amorphous carbon layer, then removing the secondamorphous carbon layer and the second nitride layer; executing a fourthtrimming etch process on the first oxide layer, the fourth trimming etchprocess being an isotropic etch that etches material of the first oxidelayer without etching material of the first amorphous carbon layer ormaterial of the first nitride layer, the fourth trimming etch processbeing executed until the width of the lines of the first oxide isreduced to one third of the line width of the second relief pattern;depositing a second fill material on the first oxide layer, the firstamorphous carbon layer and the first nitride layer; etching a portion ofthe second fill material to expose a top of the lines of the first oxidelayer; etching the lines of the first oxide layer down through the firstamorphous carbon layer, then removing the second fill material, thusforming a third relief pattern; transferring, by selective anisotropicetching, the third relief pattern into the first nitride layer, thenremoving the first amorphous carbon layer, thus forming a fourth reliefpattern; transferring, by selective anisotropic etching, the fourthrelief pattern into the memorization layer, then removing the firstnitride layer, resulting in the memorization layer having a pattern offour lines with line-to-space pitch ratio of 1:1, wherein each line andeach space has a width of one eighth of the initial line width.
 20. Themethod of claim 19, wherein each line and each space of the memorizationlayer has a width in a range of 2 to 5 nm.